The major focus (75 percent effort) of the proposed program continues the analysis of certain aspects of the synthesis of the ribosomal and transfer RNAs of prokaryotes and eukaryotes, specifically: 1. The continued analysis of the Bacillus subtilis RNase M5 as a model ribosomal RNA (rRNA) processing endonuclease. 2. The search for novel rRNA processing enzymes in B. subtilis. 3. The search for nucleolar endonucleases involved in mouse 5.8S rRNA maturation. 4. The continued analysis of the RNase P of B. subtilis as a model processing endonuclease containing protein and RNA elements. 5. The search for and analysis of RNase P from an archaebacterium. 6. The continued analysis of a substrate-specific "scavenging" nuclease from B. subtilis. A secondary focus (25 percent effort) of the proposed program will develop protocols for the use of ribosomal RNA gene cloning and sequencing to analyze, phylogenetically and quantitatively, natural microbial populations, without the necessity for establishing laboratory cultures. The specific goals of this component of the proposed project are: 7. The development of technical strategies for evaluating the phylogeny and abundance of organisms in mixed, natural populations using 16S and 5S rRNA gene cloning and sequencing. 8. The use of the developed technology to explore the microbial populations emanating from and otherwise associated with deep submarine hydrothermal vents. 9. The evaluation, using 5S rRNA sequence analysis, of the relationships of prokaryotic symbionts which confer sulfur-based chemoautotrophy on three distinct invertebrates, two of which are associated with the hydrothermal vents. 10. The examination of the nucleic acids and ribosomes of a population of hydrothermal vent microorganisms recently cultured at 300 C.